Accidental food contamination has resulted in organic mercury poisoning of pregnant women in several countries. The infants born to these women have exhibited severe central nervous system damage in many instances. Studies are underway on the localization and neuropathologic damage sustained in monkey fetuses whose mothers consumed methylmercury. Because young women can also environmentally or occupationally be exposed to phenylmercury and inorganic mercury, the placental transport and extent of fetal tissue uptake of these substances is being investigated in the macaque model. Early administration of methylmercury in the primate pregnancy is being employed to evaluate potential teratogenicity. Since penicillamine, thiol resins and selenium can lower adult tissue levels of methylmercury, their efficacy in preventing or lowering fetal tissue uptake of methylmercury is being assessed. Human fetal exposure to organic and inorganic mercury has been found to be minimal in women and their neonates in both a rural Iowa and urban Chicago population. Highest newborn and maternal levels were found to correlate with maternal age. This correlation is being studied carefully in a group of older mothers and has been extended to breast milk as well as blood levels. Correlations with possible dietary sources of mercury are also being examined. Finally, clearance rates of mercury from the simian and human newborn circulation are to be monitored.